Heat the olive oil in a large pot over medium heat.
Add the diced onion and cook until translucent, about 5 minutes.
Stir in the minced garlic and cook for an additional minute.
Add sliced carrots and diced celery, sautéing for 5–7 minutes until they begin to soften.
Incorporate the diced bell pepper and zucchini, cooking for another 3–4 minutes.
Pour in the canned diced tomatoes with their juice and vegetable broth.
Stir in the dried Italian herbs, salt, and pepper; bring to a gentle boil.
Reduce heat and let the soup simmer for 20–25 minutes.
Add the fresh spinach or kale in the last 5 minutes of cooking.
Taste and adjust seasonings if needed before serving hot.